This application claims the priority of German patent document 198 25 304, filed Jun. 5, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for regulating wheel braking in a motor vehicle.
A wheel braking regulating system of this generic type is used for example in the so-called DSC systems of BMW. (See for example ATZ-article, 1997, page 134 et seq. and page 208 et seq.). In wheel braking regulating systems of this kind the rpm of at least one wheel is regulated by selective brake applications, usually when an actual driving state differs from a specified desired driving state. The control algorithm required for this purpose is based on a mathematical vehicle model by which a specified desired driving state (for example, yaw velocity) is calculated as a function of various driving parameters, in the electronic control device which is conventionally found in wheel braking regulating systems. The vehicle model is stored as a characteristic map and/or as an algorithm.
A desired driving state is calculated by means of the vehicle model based for example, on driving parameters specified by the driver (for example steering wheel angle and accelerator position), vehicle parameters such as the center of gravity, steering behavior, tire slip rigidity, mass moment of inertia, etc. and certain environmental properties, such as the transverse slope and the changing coefficient of friction of the road. The model parameters which are used to calculate the desired driving state by means of the vehicle model are established once during the production of the vehicle. Changes in the vehicle that occur after production (for example different tires, different loading, aging of chassis parts such as shock absorbers and transverse links), in other words particularly those changes that are not covered by the vehicle parameters, are not taken into account in the calculation of the desired driving state. Consequently, the calculated specified desired driving state can differ from the actually desired driving state or from the ideal state. This degrades the system performance as a result of unnecessary and unjustified regulating interventions, with consequent adverse effects on comfort and performance disadvantages.
One object of the invention is to improve the comfort and performance of a wheel braking regulating system of the type recited at the outset.
These and other objects and advantages are achieved by the braking regulating method and apparatus according to the invention, in which a possible deviation of the calculated specified desired driving state from the ideal driving state is detected and corrected. The invention is based on the proposition that in certain driving conditions, especially during stable low-dynamic driving maneuvers, the actual driving state is identical to the ideal (desired) state, even without regulating intervention. (Conventional chassis tuning takes care of this.) Accordingly, when such driving conditions exist, there cannot be any deviation between the desired and actual momentary driving states that results in regulation. If, nevertheless, a deviation is detected in such driving conditions, the conclusion is drawn that driving parameters that are not included (and therefore are not taken into account in the vehicle model) have changed. Then, automatic correction of the vehicle model corresponding to the deviation is brought about in the electronic control device. This correction is preferably maintained until another correction is made.
According to the invention, at least one condition is defined as an indication that the current actual driving state exists that should be identical with an ideal (desired) driving state. One such condition for example is that the vehicle speed is at least approximately constant. Another is that the steering angle velocity, the transverse acceleration, the actual yaw velocity and/or the deviation of a measured actual yaw velocity from a calculated yaw velocity, in each case is below a specified threshold.
It is important that the correction of the vehicle model should be made only in a driving state in which the assumption that the actual driving state is identical with the ideal driving state, is in fact correct.
In the wheel braking regulating system according to the invention, with automatic correction of the vehicle model, optimum comfort is ensured both over a prolonged period of time (for example, the aging processes) and also during changes in vehicle properties (for example, different tires). A possible feeling of uncertainty on the part of the driver caused by unjustified regulating interventions or by deteriorated system performance is prevented as well.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.